The 28-year-old right-hander had just completed a 1-2-3 fifth inning and was taking the mound for the sixth. On the first warmup pitch he fired toward home plate, he felt something in his back.

"It just happened really quick," Norris said after the Astros' 7-2 loss at Comerica Park. "I went out there and threw the first warmup pitch and it happened real fast. A sky-high fastball and it just kind of tweaked me. I threw a couple more pitches that were all right, but I didn't get better any faster."

Manager Bo Porter and trainer Nate Lucero, who had been on the field earlier in the game to attend to Altuve after a collision in right field, jogged out to the mound to check on their starter.

Although Norris asked to remain in the game, Porter argued there would be no point in risking further injury to what has surely been the team's best pitcher thus far.

"It's just one of those things where he let the ball go, and he tried to talk his way into [staying in], but I said, 'No way.'" the skipper said. "There's no sense in it. If he already tweaked it or feels something at that point in the game, it's better to get off.

"It's a cold night, there's just no telling what would happen if you continue to try to go on."

Norris had surrendered seven runs in five innings on nine hits and two walks until that point -- including his first career grand slam allowed. However, with only 71 pitches thrown, he likely could've remained in the game an inning or two longer.

Norris, now 4-4 with a 4.32 ERA, said he will sleep on it and see how it feels in the morning. As he stood talking to the media following the game, he said he still felt some discomfort.

"I'll see how it goes from there," Norris said.

Said Porter: "It will probably be more telling when he shows up to the park tomorrow and he'll be evaluated by the training staff."

Anthony Odoardi is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.